This invention relates to hub clutches and more particularly to a hub clutch for front wheels of a four-wheel drive vehicle, wherein there is no necessity for a driver of a vehicle operating the hub clutch from the exterior of the vehicle.
Normally such front wheels receive a driving force from a road surface during rear-wheel drive running periods. It is desirable during such periods that the front wheels be free-rolling when they are not being driven in order to reduce drag on the engine, to prevent rotation of the driving shafts, gears, etc. and to avoid unnecessary wear for improving running efficiency and fuel consumption. Therefore, it is required to provide an apparatus or hub clutch for preventing transfer of the driving force from the road surface to the components back to the front wheels.
The hub clutch developed for such a demand includes, for example, the following:
FIG. 1 is a schematic sectional view of the hub clutch which is disclosed in my pending application, U.S. Ser. No. 968,356. This hub clutch has features in that a shaft portion 112a of a bolt 112 to secure a case 110 to a wheel hub 111 is partially exposed on the inner surface of the case 100. The exposed shaft portion 112a is slidably engaged a groove 114 formed on the outer periphery of a driven clutch 113 adapted to be coupled with a drive clutch 115. The torque of the driven clutch 113 is directly transferred to the bolt 112 and then to the wheel hub 111 through the bolt 112. According to this invention, it is unnecessary to give a torque transfer function to the case itself and consequently, it is possible to use a lower strength and lighter weight material such as a light alloy for the case 110. This results in a light weight hub clutch. Since it is also not necessary to form a spline on the inner periphery of the case 110, the case easily may be manufactured in fewer process operations, and the driven clutch 113 has a space with a larger inner diameter so that it is easy to install other parts therein and the hub clutch becomes smaller in size.
However, this prior hub clutch has a disadvantage that an operator must get off the vehicle to switch a selecting lever 120 by a manual operation upon the clutch on-off operation, i.e., the switchover from four-wheel drive to two-wheel drive or vice versa.
FIG. 2A is a partly sectional fragmentary elevation view of a hub clutch disclosed in U.S. Pat. No. 2,884,101. FIG. 2B is a cross-sectional view taken of line A-A along FIG. 2A. This clutch comprises a polygonal sleeve or cylindrical cam 220 fitted to a drive shaft 212, a cylindrical case 228 disposed radially outwardly of the cam 220 and fixed to a hub 217 by means of bolt 276, a plurality of rollers 224 disposed between the cam 220 and the case 228 and positioned in a retainer or roller cage 226 at equal intervals therearound, and a spring 234.
Unless external force is applied to the retainer clockwise or counterclockwise, a weak contact situation is maintained by means of the spring and power transmission is not effected. By switching a selecting lever from a two-wheel drive side over to a four-wheel drive side, the drive shaft, i.e. the cam, is rotated, the retainer is not rotated because an auxiliary friction member contacts with a stationary system, and the roller is wedged in between the cam and case, thereby power transmission is carried out. When the selective lever is changed over to return to the two-wheel drive side, the retainer is returned to the original position due to no rotation of the drive shaft, thereby cutting off power transmission. In this way, this hub clutch accomplishes a changeover operation thereof by shifting a relative position between the cam and the retainer to move the rollers, and therefore the connection and disconnection of the hub clutch can be easily and surely achieved.
In this prior hub clutch referred to as automatic, there have been observed several disadvantages as follows:
(1) an engine brake may fail to work, and thus upon off-load running, a driver must get off the vehicle and turn a manually operating selective lever 270 to lock it for working the engine brake; (2) the structures including the locking mechanism are very complicated; (3) it is not durable and heavy.